JP6760105B2 - Arc failure detector - Google Patents

Description

The present invention relates to an arc failure detection device for detecting an arc generated in a branch system in a DC power generation system such as a photovoltaic power generation system or a DC power supply system.

The following are proposed as conventional techniques for detecting an arc in a DC circuit such as a photovoltaic power generation system.
For example, in the arc detecting means described in Patent Document 1, it is considered that an arc is generated, a short circuit, and a disconnection failure occur due to forgetting to tighten a screw in a terminal block connected to a solar cell panel, and the output side from the terminal block. The fluctuation of the voltage between the wiring and the fluctuation of the current flowing from the terminal block to the output side wiring are detected at the same time.

Further, the arc detection device described in Patent Document 2 has a large number of solar cell panels and is arranged at a plurality of locations like a mega solar, and the switching noise of the inverter of the power conditioner (PCS) is superimposed. It is premised on application to such DC circuits.
In this arc detection device, the voltage across a DC circuit in which a plurality of solar cell panels are connected in series is detected, the output is converted into a power spectrum, and then the frequency band corresponding to the switching noise of the inverter is removed and removed. When the gradient of the power spectrum obtained at a plurality of points of the subsequent power spectrum exceeds a predetermined reference value, the generation of an arc in the DC circuit is determined.

In the prior art described in Patent Document 1, in principle, an arc is generated in the vicinity of the terminal block, in other words, in the vicinity of the voltage sensor, and can be detected when the voltage or the like fluctuates. However, especially in a large-scale photovoltaic power generation system such as a mega solar, since the cables are laid over a long distance, arc failures due to disconnection of the cables may occur at various places.
For this reason, it is difficult to detect an arc failure that occurs in a cable or the like on the solar cell panel side of the terminal block because there is almost no sudden voltage fluctuation at the installation position of the voltage sensor near the terminal block.

Further, the conventional technique described in Patent Document 2 is a detection method focusing on a high frequency component of a voltage generated when an arc is generated, and a failure has occurred among a plurality of branch systems (strings) connected to the main system. In order to distinguish between a grid and a healthy grid, it is necessary to have a photovoltaic power generation system with a backflow prevention diode.
In Japan, photovoltaic power generation systems equipped with the above-mentioned backflow prevention diode are becoming mainstream.

Japanese Unexamined Patent Publication No. 2011-7765 (paragraphs [0031] to [0040], FIGS. 1 to 3, etc.) Japanese Unexamined Patent Publication No. 2014-134445 (paragraphs [0012] to [0014], FIG. 1, etc.)

On the other hand, in the global mainstream of photovoltaic power generation systems in recent years, PV fuses are used as a safety measure against backflow without using a backflow prevention diode. According to this type of system, since the detection method described in Patent Document 2 cannot distinguish between a failed system and a healthy system, it is necessary to stop the entire system when a failure occurs, and it takes a lot of time to identify and recover the failure point. It took time and effort.
That is, it was not possible to determine the faulty system depending on the configuration of the photovoltaic power generation system, and it was difficult to stably continue the photovoltaic power generation.

In a photovoltaic power generation system, the characteristics at the time of an arc failure differ depending on the presence or absence of a backflow prevention diode, so the configuration of the arc failure detection device must be different, but from the viewpoint of versatility, the mainstream backflow prevention in Japan There is a need to realize an arc failure detection device that can handle both systems with diodes and systems without backflow prevention diodes, which are the mainstream in the world.
However, at present, it is difficult to detect an arc failure under the same circuit configuration and signal processing method regardless of the presence or absence of a backflow prevention diode, and it is desired to realize an arc failure detection device that enables this. It was rare.

Therefore, the problem to be solved by the present invention is to provide an arc failure detection device capable of reliably detecting an arc failure of a branch system by the same circuit configuration and signal processing method regardless of the presence or absence of a backflow prevention element such as a diode. It is in.

In order to solve the above problem, the invention according to claim 1 is connected to a DC bus connected to an AC power supply system via a power conditioner, and the power generated by the DC power generation facility is transferred via a pair of branch lines. In the arc failure detection device in the branch system supplied to the DC bus,
A current detecting means for detecting a DC component and an AC component of the current flowing through one of the branch lines, and
A first voltage detecting means capable of detecting a voltage between two points on one of the branch lines,
A second voltage detecting means for detecting the voltage between the pair of branch lines, and
A DC component current threshold value determining means that compares the DC component of the current detected by the current detecting means with a predetermined threshold value.
An AC component current threshold value determining means that compares the AC component of the current detected by the current detecting means with a predetermined threshold value.
A voltage threshold value determining means for comparing the voltage detected by the first voltage detecting means and the voltage detected by the second voltage detecting means with a predetermined threshold value, respectively.
The arc failure in the branch system is determined based on the logical operation result obtained by combining the output of the DC component current threshold value determination means and the output of the voltage threshold value determination means and the determination result by the AC component current threshold value determination means. Failure determination means to be performed and
It is characterized by being equipped with.

The invention according to claim 2 is the backflow prevention element for blocking a direct current in the direction from the direct current bus to the direct current power generation facility at one of the branch lines in the arc failure detection device according to claim 1. Is connected, and the first voltage detecting means detects the voltage across the backflow prevention element.

According to the third aspect of the present invention, in the arc failure detection device according to the first aspect, a backflow prevention element for blocking a direct current in a direction from the direct current bus to the direct current power generation facility is provided on one of the branch lines. It is characterized in that the input terminals of the first voltage detecting means are short-circuited when they are not connected.

The invention according to claim 4 is the arc failure detection device according to any one of claims 1 to 3, wherein the failure determination means is based on the determination result by the AC component current threshold determination means. It is characterized in that the series arc failure generated in the branch line is determined.

The invention according to claim 5 is the arc failure detecting device according to any one of claims 1 to 4, wherein the failure determining means uses the output of the first voltage detecting means to determine the voltage threshold value. The logical sum of the determination result by the DC component current threshold determination means and the reverse current determination result by the DC component current threshold determination means, and the determination result by the voltage threshold determination means using the output of the second voltage detection means and the DC component. It is characterized in that the parallel arc failure generated between the pair of branch lines is determined based on the logical product of the determination result of the forward current by the current threshold determination means.

The invention according to claim 6 is a logical calculation in which the output of the DC component current threshold determination means and the output of the voltage threshold determination means are combined in the arc failure detection device according to any one of claims 1 to 5. Further, a first timer means for setting a time limit for the result and a second timer means for setting a time limit for the determination result by the AC component current threshold value determination means are further provided, and the failure determination means is the first timer means. It is characterized in that the arc failure in the branch system is determined based on the output of the second timer means.

The invention according to claim 7 is the disconnector for disconnecting the main system connected between the power conditioner and the DC bus in the arc failure detection device according to any one of claims 1 to 6. Further, the disconnecting switch for the branch system connected to the branch system is further provided, and the failure determining means opens the disconnecting switch for the main system or the disconnecting switch for the branch system at the time of determining the arc failure. It is characterized by having a function to perform.

According to the present invention, an arc failure can be reliably detected regardless of the presence or absence of a backflow prevention element in the branch system, the failure location can be separated and protected, and the power supply from the sound system can be continued.

It is a block diagram of the photovoltaic power generation system to which 1st Embodiment of this invention is applied. It is a block diagram which shows the structure of the arc failure detection apparatus which concerns on 1st Embodiment of this invention. FIG. 1 is an explanatory diagram of a current path when a series arc 501 is generated. It is a waveform diagram which shows the voltage signal and the current signal of each part at the time of the serial arc 501 generation. It is a figure which shows the operation of the voltage threshold value determination circuit, the current threshold value determination circuit, etc. at the time of arc generation. FIG. 1 is an explanatory diagram of a current path when a parallel arc 502 is generated. It is a waveform diagram which shows the voltage signal and the current signal of each part when the parallel arc 502 is generated. FIG. 1 is an explanatory diagram of a current path when a parallel arc 503 is generated. It is a waveform diagram which shows the voltage signal and the current signal of each part at the time of parallel arc 503 generation. It is a block diagram of the photovoltaic power generation system to which the 2nd Embodiment of this invention is applied. It is a block diagram which shows the structure of the arc failure detection apparatus which concerns on 2nd Embodiment of this invention. FIG. 10 is an explanatory diagram of a current path when a parallel arc 502 is generated. It is a waveform diagram which shows the voltage signal and the current signal of each part when the parallel arc 502 is generated. FIG. 10 is an explanatory diagram of a current path when a parallel arc 503 is generated. It is a waveform diagram which shows the voltage signal and the current signal of each part at the time of parallel arc 503 generation. It is a block diagram which shows the structure of the arc failure detection apparatus which concerns on 3rd Embodiment of this invention. It is a block diagram which shows the structure of the arc failure detection apparatus which concerns on 4th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a photovoltaic power generation system to which the first embodiment of the present invention is applied. In FIG. 1, 1 is an AC power supply system, 2 is a power conditioner (PCS), 3 is a disconnector for a main system, and 4 is a DC bus composed of a positive bus P and a negative bus N. Branch lines 5A and 5B having the same configuration are connected to the bus 4 in parallel with each other.
The system from the DC bus 4 to the PCS2 is referred to as a main system with respect to the branch systems 5A and 5B.

Next, the configuration of the branch system 5A will be described.
This branch system 5A has a solar cell panel 104 as a DC power generation facility connected to a positive bus P and a negative bus N constituting the DC bus 4 via a pair of branch lines 41, and also has a positive bus P. It is provided with a backflow prevention diode (hereinafter, also simply referred to as a diode) 101 to which a cathode is connected to the busbar, a switch 102 for disconnection, and a switch 103 for short circuit.
Further, the branch system 5A includes a current detection device 105 that detects an AC component and a DC component of the current flowing through one branch line 41, a voltage detection device 106 that detects the voltage across the diode 101, and a pair of branch lines 41. A voltage detection device 107 for detecting the voltage between the and 41 and a determination circuit 111 for inputting the detection values of the detection devices 105 to 107 to determine the arc failure are provided.
Similarly, the branch system 5B also has a pair of branch lines 42, a diode 201, a disconnecting switch 202, a short-circuit switch 203, a solar panel 204, a current detection device 205, a voltage detection devices 206, 207, and a determination circuit 211. It has.

In the above configuration, the detection devices 105 to 107 and the determination circuit 111 of the branch system 5A, and the detection devices 205 to 207 and the determination circuit 211 of the branch system 5B, respectively, constitute the main part of the arc failure detection device in the present embodiment. are doing.
Next, a specific configuration of the arc failure detection device of the branch system 5A (the same applies to the branch system 5B) will be described with reference to FIG.

In FIG. 2, a voltage divider 112 is connected to both ends of the diode 101, and an insulating amplifier 114, a low-pass filter (LPF) 116, and a first voltage threshold determination circuit 121 are sequentially connected to the output side thereof. Further, a voltage divider 113 is connected between the branch lines 41 and 41 connected to the solar cell panel 104 (not shown), and an insulation amplifier 115, an LPF 117, and a second voltage threshold value determination circuit 122 are connected to the output side thereof. They are connected sequentially.

Further, a current transformer (CT) 301 is provided on one of the branch lines 41, and the output thereof is input to the LPF 118 and the bandpass filter (BPF) 119.
The output of the LPF 118 is input to the first and second current threshold voltage determination circuits 123 and 124, and the output of the BPF 119 is input to the third current threshold voltage determination circuit 125 via the rectifier circuit 120.
Here, the first and second current threshold determination circuits 123 and 124 constitute the DC component current threshold determination means according to the claim, and the third current threshold determination circuit 125 constitutes the AC component current threshold determination means according to the claim. Consists of.

The output of the first voltage threshold value determination circuit 121 and the output of the first current threshold value determination circuit 123 are input to the determination output unit 131 via the ore gate 126 and the first timer circuit 128 in sequence. Further, the output of the second voltage threshold value determination circuit 122 and the output of the second current threshold value determination circuit 124 are sequentially input to the determination output unit 131 via the and gate 127 and the second timer circuit 129.
Further, the output of the third current threshold value determination circuit 125 is input to the determination output unit 131 via the third timer circuit 130.

The determination output unit 131 determines the presence / absence and type of arc failure based on the output signals of the first to third timer circuits 128 to 130, displays the result by the status display circuit 131a, and by the protection control circuit 131b. It controls the opening and closing of the disconnecting switch and short-circuit switch to protect the system.
In FIG. 2, the power supply circuit for supplying power to each part is not shown.

Next, the operation of this embodiment will be described.
In order to make the voltage of several hundred [V] to 1 [kV] between the branch lines 41 and 41 in FIG. 2 large enough to be processed by the subsequent electronic circuit, the detection voltage is lowered by the voltage dividers 112 and 113. By passing the LPF 116, 117 through the insulation amplifiers 114, 115, unnecessary high frequency noise components are removed.
Further, the DC component of the current of the branch line 41 detected by CT301 is detected by LPF118, and the AC component is detected by BPF119. Here, in BPF119, in order to detect a high frequency component and remove an unnecessary noise component, a frequency component of 1 [kHz] to 100 [kHz] is extracted.

The first voltage threshold value determination circuit 121 outputs an “H” (High) level signal when the input signal is equal to or higher than a predetermined threshold value, and the second voltage threshold value determination circuit 122 outputs an “H” (High) level signal, and the second voltage threshold value determination circuit 122 outputs the input signal to a predetermined threshold value. If it is less than, an "H" level signal is output.
The first current threshold value determination circuit 123 detects that the current energization direction is opposite, and outputs, for example, an “H” level signal when the input signal is less than a predetermined threshold value. The second current threshold value determination circuit 124 detects that the current energization direction is the forward direction, and outputs an “H” level signal when the input signal is equal to or higher than a predetermined threshold value. The third current threshold value determination circuit 125 outputs an “H” level signal when the signal after full-wave rectification of the BPF 119 signal by the rectifier circuit 120 becomes equal to or higher than a predetermined threshold value.

In the logic calculation unit provided on the output side of the above-mentioned voltage and current threshold voltage determination circuits 121 to 125, the logical sum of the determination result by the first voltage threshold voltage determination circuit 121 and the determination result by the first current threshold voltage determination circuit 123. Is obtained by the or gate 126, and the logical product of the judgment result by the second voltage threshold voltage judgment circuit 122 and the judgment result by the second current threshold voltage judgment circuit 124 is obtained by the and gate 127, and when true, the "H" level is obtained. Output each signal.
The output of the or gate 126, the output of the AND gate 127, and the output of the third current threshold value determination circuit 125 are such that the timer circuits 128 to 130 each output an "H" level signal when they continue for a certain period of time. It has become.

The time periods of the timer circuits 128 to 130 are set in the range of several [ms] to several hundreds [ms], and each time period is timer circuit 129 <128 <130, and the output from the timer circuit 129 is output. The order is the earliest, followed by the timer circuit 128 and the timer circuit 130.
The timer circuits 128 and 129 correspond to the first timer means in the claim, and the timer circuit 130 corresponds to the second timer means in the claim.

As will be described in detail later, the determination output unit 131 determines that some arc failure has occurred when any of the output signals of the timer circuits 128 to 130 reaches the “H” level, and the status display circuit 131a and the protection The control circuit 131b performs a status display operation and a protection control operation according to the determination result.
In the above configuration, the or gate 126, the AND gate 127, the timer circuits 128 to 130, and the determination output unit 131 constitute the failure determination means according to the claim.

Next, a specific detection operation when an arc failure occurs will be described.
FIG. 3 shows a case where one branch line 41 in the branch system 5A is disconnected to generate a series arc 501, and reference numeral a is a current path from the solar cell panel 104. An arc generated on a single branch line is called a series arc, and an arc generated between positive and negative branch lines is called a parallel arc.
By the series arc 501 of FIG. 3, the power generated by the solar panel 104 is supplied from the disconnecting switch 102 to the PCS2 via the disconnecting switch 102, the arc failure detection device of the present embodiment including the determination circuit 111, and the disconnecting switch 3. ..

FIG. 4 is a waveform diagram showing the voltage signal and current signal of each part when the series arc 501 is generated, and the voltage signals (1) and (2) are the outputs of LPF116 and 117, and the current signals (1) and (2), respectively. 2) shows the output of LPF118, and the current signal (3) shows the output of BPF119. In FIG. 4, the series arc 501 is generated at time 0.
FIG. 5 shows the operations of the voltage threshold value determination circuits 121 and 122, the current threshold value determination circuits 123 to 125, and the like when an arc failure occurs, and the reference numerals A to E in the left column are the outputs of the determination circuits 121 to 125, respectively. Similarly, the reference numerals α, β, and γ are inputs of the timer circuits 128, 129, and 130, respectively.
When the series arc 501 of FIG. 4 occurs, the operation is as shown in "Failure mode (1) Series arc failure (a) System with backflow prevention diode" in FIG.

When the series arc 501 is generated, a forward current continues to flow in the diode 101, so that the voltage signal (1) (output of the LPF 116) is less than the threshold even when the voltage drop of the diode 101 is taken into consideration, as shown in FIG. Therefore, the output of the voltage threshold determination circuit 121 is at the “L” (Low) level.
Further, since the line voltage of the branch line 41 is almost unchanged from the operating voltage equivalent to the sound state (about several hundred [V] to 1 [kV]), the voltage signal (2) (output of LPF117) is above the threshold value. Yes, the output of the voltage threshold determination circuit 122 is also at the "L" level.

Further, since the current continues to flow in the same direction (forward direction) as when it is sound, the current signals (1) and (2) (output of LPF118), which are DC components of the current, indicate the forward direction. In FIG. 4, the current signals (1) and (2) have 1.5 as a reference value, and the case where the current signal is greater than or equal to the reference value is defined as the forward direction, and the case where the current signal is less than the reference value is defined as the reverse direction.
Therefore, the current threshold value determination circuit 123 outputs an “L” level signal, and the current threshold value determination circuit 124 outputs an “H” level signal.

Further, since the current includes a high frequency component (arc noise) which is a peculiar signal at the time of arc generation, the current signal (3) (output of BPF119) which is an AC component of the current becomes large after the failure occurs. Therefore, when the reference of the current signal (3) is shifted to 0 and then full-wave rectified by the rectifier circuit 120, the current signal (3) in FIG. 4 becomes the signal after rectification and becomes a value equal to or higher than the threshold value. An “H” level signal is output from the threshold determination circuit 125.

As a result, the outputs of the or gate 126 and the AND gate 127 become the "L" level, and the "H" level signal is output after the set time period by the timer circuit 130 on the output side of the current threshold value determination circuit 125 has elapsed. Based on this "H" level signal, the output determination unit 131 determines that the series arc failure 501, and then opens the disconnect switch 102 to remove the accident point from the branch system 5A.

Next, FIG. 6 shows a case where the pair of branch lines 41 and 41 are short-circuited between the solar cell panel 104 of the branch system 5A and the short-circuit switch 103, and a parallel arc 502 is generated. Reference numeral b is a current path from the solar cell panel 104 passing through the parallel arc 502.
In this case, since the diode 101 exists in the branch system 5A, no current flows from the branch system 5B, which is a healthy system, to the failure point, and the PCS 2 maintains the normal operation.

The operation when the parallel arc 502 of FIG. 6 is generated will be described with reference to FIGS. 5 and 7. The operation of this case is shown in "Failure mode (2) Parallel arc failure (a) System with backflow prevention diode" in FIG. Further, in FIG. 7, the parallel arc 502 is generated at time 0.

Due to the generation of the parallel arc 502, the line voltage of the branch line 41 drops to the equivalent of the arc voltage (several tens [V]), while the line voltage of the DC bus 4 via the diode 101 is the operating voltage (when sound). It maintains several hundred [V] to 1 [kV]).
Therefore, the voltage signal (1) (output of LPF116) in FIG. 7 becomes equal to or higher than the threshold value, and the output of the voltage threshold value determination circuit 121 becomes “H” level. Further, since the line voltage of the branch line 41 drops to the equivalent of the arc voltage, the voltage signal (2) (output of LPF117) becomes less than the threshold value, and the output of the voltage threshold value determination circuit 122 also becomes the “H” level.

Further, since no current flows through the current transformer 301, the current signals (1) and (2) (output of LPF118) are 1.5, which corresponds to zero current. Therefore, the outputs of the current threshold value determination circuits 123 and 124 are at the "L" level. Further, since no current flows, the current signal (3) (output of BPF119) and the signal after rectification thereof also become less than the threshold value, and the output of the current threshold value determination circuit 125 becomes the “L” level.

Therefore, the output of the or gate 126 is at the "H" level, the output of the AND gate 127 is at the "L" level, and after a predetermined time period has elapsed, a signal of the "H" level is output from the timer circuit 128.
As a result, the determination output unit 131 detects the occurrence of the parallel arc 502, opens the disconnect switch 102, and short-circuits the short-circuit switch 103 to form a current path having a lower impedance than the arc failure point. Control is performed to eliminate the accident point by erasing the parallel arc 502.

Next, FIG. 8 shows a case where the pair of branch lines 41 and 41 are short-circuited between the diode 101 of the branch system 5A and the disconnect switch 102, and a parallel arc 503 is generated.
In FIG. 8, reference numeral c is a current path by the other sound branch system 5B, and since the diode 101 is present in the one branch system 5A, no current flows from the branch system 5B to the failure point, and PCS2 Maintains normal operation. Reference numeral d is a current path via the parallel arc 503 in the branch system 5A.

The operation when the parallel arc 503 of FIG. 8 is generated will be described with reference to FIGS. 5 and 9. The operation of this case is shown in "Failure mode (3) Parallel arc failure (a) System with backflow prevention diode" in FIG. Further, in FIG. 9, the parallel arc 502 is generated at time 0.

When the parallel arc 503 is generated, the voltage signals (1) and (2) in FIG. 9 show the same behavior as the voltage signals (1) and (2) in FIG. 7 when the parallel arc 502 is generated, respectively. The outputs of the threshold value determination circuits 121 and 122 are both at the "H" level.
Further, since the current continues to flow in the same direction (forward direction) as in the sound state, the current signals (1) and (2) in FIG. 9 are the current signals (1) and (2) in FIG. 4 when the series arc 501 is generated. It shows the same behavior as 2). Therefore, the current threshold value determination circuit 123 outputs an “L” level signal, and the current threshold value determination circuit 124 outputs an “H” level signal.
Further, the current signal (3) (output of BPF119), which is an AC component of the current, becomes large as in FIG. 4, and an “H” level signal is output from the current threshold value determination circuit 125.

As a result, the outputs of the or gate 126 and the AND gate 127 are both at the "H" level. Here, the determination output unit 131 detects that the parallel arc 503 has occurred based on the fact that the output of the timer circuit 129, which has the shortest time period among the timer circuits 128 to 130, first reaches the “H” level. ..
For this failure, the determination output unit 131 controls to open the disconnect switch 102 to disconnect the accident point.

Next, the configuration and operation of the arc failure detection device according to the second embodiment will be described for a photovoltaic power generation system in which the backflow prevention diode is not provided in the branch system.
FIG. 10 shows a configuration of a photovoltaic power generation system to which the second embodiment is applied, and FIG. 11 is a block diagram of an arc failure detection device. The difference between FIGS. 10 and 11 from FIGS. 1 and 2 described above is that the branch systems 5A'and 5B' are not provided with a backflow prevention diode, and the voltage detector 106 of FIG. 10 (voltage divider 112 of FIG. 11). ) Is short-circuited between the input terminals, and the other configurations are the same as those in FIGS. 1 and 2, so the description thereof will be omitted.

Next, a specific arc failure detection operation will be described.
The series arc detection operation in the branch system is the same as in FIGS. 3 and 4 and the like described in the case where the branch system has a diode. That is, the operations of the determination circuits 121 to 125, the timer circuits 128 to 130, and the like are as in the "failure form (1) series arc failure (b) system without backflow prevention diode" in FIG.

FIG. 12 shows a case where the pair of branch lines 41 and 41 are short-circuited between the solar cell panel 104 of the branch system 5A'and the short-circuit switch 103, and a parallel arc 502 is generated. Reference numeral b is a current path from the solar cell panel 104 passing through the parallel arc 502. Further, since there is no diode in the branch system 5A', a current flows from the sound branch system 5B'to the branch system 5A' to form a current path e passing through the parallel arc 502, and the PCS2 stops operating.

The operation when the parallel arc 502 of FIG. 12 is generated will be described with reference to FIGS. 5 and 13. The operation of this case is shown in "Failure mode (2) Parallel arc failure (b) System without backflow prevention diode" in FIG. Further, in FIG. 13, the parallel arc 502 is generated at time 0.

Due to the generation of the parallel arc 502, the line voltage of the branch line 41 drops to the equivalent of the arc voltage (several tens [V]). Here, since the input terminals of the voltage divider 112 are short-circuited, the voltage signal (1) (output of the LPF 116) becomes less than the threshold value, and the output of the voltage threshold value determination circuit 121 becomes the “L” level. At the same time, the voltage signal (2) (output of LPF117) also becomes less than the threshold value, and the output of the voltage threshold value determination circuit 122 becomes the “H” level.

Further, a current in the opposite direction continues to flow in the current transformer 301 toward the parallel arc 502. As a result, the current signals (1) and (2) (output of LPF118), which are DC components, become less than the threshold value, the output of the current threshold value determination circuit 123 becomes the "H" level, and the output of the current threshold value determination circuit 124 becomes "H" level. It becomes "L" level. Further, the signal after full-wave rectification of the current signal (3) (output of BPF119) becomes equal to or higher than the threshold value, and the output of the current threshold value determination circuit 125 becomes “H” level.

Therefore, the output of the or gate 126 is at the "H" level, and the output of the AND gate 127 is at the "L" level. Here, in the timer circuit 128 and the timer circuit 130, the time limit of the timer circuit 128 is shorter, and the "H" level signal is output first. Therefore, the determination output unit 131 uses this "H" level signal. Based on this, the generation of the parallel arc 502 is detected.
After that, the determination output unit 131 opens the disconnect switch 102 and short-circuits the short-circuit switch 103 to form a current path having a lower impedance than the arc failure point, thereby erasing the parallel arc 502 and eliminating the accident point. Control to remove.

Next, FIG. 14 shows a case where the pair of branch lines 41 and 41 are short-circuited between the DC bus 4 and the disconnect switch 102 in the branch system 5A', and a parallel arc 503 is generated.
In FIG. 14, reference numeral d is a current path from the solar cell panel 104 passing through the parallel arc 503. Further, since there is no diode in the branch system 5A', a current flows from the sound branch system 5B' and a current path f passing through the parallel arc 503 is formed, and the PCS2 stops operating.

The operation when the parallel arc 503 of FIG. 14 is generated will be described with reference to FIGS. 5 and 15. The operation of this case is shown in "Failure mode (3) Parallel arc failure (a) System without backflow prevention diode" in FIG. Further, in FIG. 15, the parallel arc 503 is generated at time 0.

Since the line voltage of the branch line 41 drops to the equivalent of the arc voltage (several tens [V]) due to the generation of the parallel arc 503, the voltage signal (1) is the same as when the parallel arc 502 is generated as shown in FIG. (Output of LPF116) becomes less than the threshold value, and the output of the voltage threshold value determination circuit 121 becomes the “L” level. At the same time, the voltage signal (2) (output of LPF117) also becomes less than the threshold value, and the output of the voltage threshold value determination circuit 122 becomes the “H” level.

Unlike FIG. 12, a forward current continues to flow in the current transformer 301.
As a result, the current signals (1) and (2) (output of the LPF 118), which are DC components, become equal to or higher than the threshold value, so that the output of the current threshold value determination circuit 123 becomes the “L” level, and the output of the current threshold value determination circuit 124 becomes. It becomes "H" level. Further, the signal after full-wave rectification of the current signal (3) (output of BPF119) becomes equal to or higher than the threshold value, and the output of the current threshold value determination circuit 125 becomes “H” level.

Therefore, the output of the or gate 126 is at the "L" level, and the output of the AND gate 127 is at the "H" level. Here, in the timer circuit 129 and the timer circuit 130, the time limit of the timer circuit 129 is shorter and the "H" level signal is output first, so that the determination output unit 131 outputs the "H" level signal to this "H" level signal. Based on this, the generation of the parallel arc 503 is detected, and the disconnect switch 102 is opened to control the removal of the accident point.
Further, since the current path d of the branch system 5A'formed by the parallel arc 503 and the current path f of the branch system 5B'are electrically equivalent, the current detection device 205 and the voltage detection device 206 of the branch system 5B' , 207, the determination circuit 211 operates in the same manner as the branch system 5A'side, and the disconnect switch 202 is opened.

In FIGS. 2 and 11, the current transformer 301 is used as the current detection device, but as shown in the third embodiment of FIG. 16, a shunt resistor 302 is used as the current detection device, and the current transformer 132 is used. It may be connected to LPF118 and BPF119.
Further, in the current transformer 301 in FIGS. 2 and 11 and the shunt resistor 302 in FIG. 16, the DC component and the AC component of the current are collectively detected, but as shown in the fourth embodiment of FIG. 17, 2 LPF118 and BPF119 may be connected to the current transformers 301a and 301b (or two shunt resistors), respectively, and the DC component and the AC component of the current may be detected separately.

The present invention is applicable to detect a series arc failure or a parallel arc failure in a branch system and perform a protective operation regardless of the presence or absence of a backflow prevention diode. Further, the DC power generation facility included in the branch system may be a DC power source other than the solar panel, in other words, the present invention can be used for various DC power generation systems and DC power supply systems including a solar power generation system.

1: AC power supply system 2: PCS (power conditioner)
3: Disconnector switch 4: DC bus 5A, 5A', 5B, 5B': Branch system 41, 42: Branch line 101, 201: Backflow prevention diode (backflow prevention element)
102, 202: Switch for disconnection 103, 203: Switch for short circuit 104, 204: Solar cell panel (DC power generation equipment)
105, 205: Current detector 106, 107, 206, 207: Voltage detector 111, 211: Judgment circuit 112, 113: Voltage divider 114, 115, 132: Insulation amplifier 116, 117, 118: Low-pass filter (LPF)
119: Bandpass filter (BPF)
120: Rectifier circuit 121, 122: Voltage threshold determination circuit 123, 124, 125: Current threshold determination circuit 126: Orgate 127: And gate 128 to 130: Timer circuit 131: Judgment output unit 131a: Status display circuit 131b: Protection control circuit 301, 301a, 301b: Current transformer (CT)
302: Shunt resistance 501: Series arc 502,503: Parallel arc P: Positive busbar N: Negative busbar

Claims (7)

In an arc failure detection device in a branch system connected to a DC bus connected to an AC power system via a power conditioner and supplying power generated by a DC power generation facility to the DC bus via a pair of branch lines.
A current detecting means for detecting a DC component and an AC component of the current flowing through one of the branch lines, and
A first voltage detecting means capable of detecting a voltage between two points on one of the branch lines,
A second voltage detecting means for detecting the voltage between the pair of branch lines, and
A DC component current threshold value determining means that compares the DC component of the current detected by the current detecting means with a predetermined threshold value.
An AC component current threshold value determining means that compares the AC component of the current detected by the current detecting means with a predetermined threshold value.
A voltage threshold value determining means for comparing the voltage detected by the first voltage detecting means and the voltage detected by the second voltage detecting means with a predetermined threshold value, respectively.
The arc failure in the branch system is determined based on the logical operation result obtained by combining the output of the DC component current threshold value determination means and the output of the voltage threshold value determination means and the determination result by the AC component current threshold value determination means. Failure determination means to be performed and
An arc failure detection device characterized by being equipped with. In the arc failure detection device according to claim 1,
A backflow prevention element for blocking a direct current in the direction from the DC bus to the DC power generation facility is connected to the branch line.
The first voltage detecting means is an arc failure detecting device characterized by detecting a voltage across the backflow prevention element. In the arc failure detection device according to claim 1,
When the backflow prevention element for blocking the DC current in the direction from the DC bus to the DC power generation facility is not connected to the branch line, the input terminals of the first voltage detecting means are short-circuited. An arc failure detection device characterized by this. In the arc failure detection device according to any one of claims 1 to 3,
The failure determination means
An arc failure detecting device for determining a series arc failure generated in one of the branch lines based on a determination result by the current threshold value determining means for an AC component. In the arc failure detection device according to any one of claims 1 to 4.
The failure determination means
The logical sum of the determination result by the voltage threshold voltage determining means using the output of the first voltage detecting means and the determination result of the reverse current by the DC component current threshold value determining means, and the second voltage detecting means. Based on the logical product of the determination result by the voltage threshold voltage determination means using the output of the above and the determination result of the forward current by the DC component current threshold determination means, the parallel arc failure generated between the pair of branch lines is detected. An arc failure detection device characterized by making a determination. In the arc failure detection device according to any one of claims 1 to 5.
A time is provided for the first timer means for setting a time limit for the logical operation result obtained by combining the output of the DC component current threshold value determining means and the output of the voltage threshold value determining means, and for the determination result by the AC component current threshold value determining means. Further equipped with a second timer means,
The failure determination means is an arc failure detection device that determines an arc failure in the branch system based on the outputs of the first timer means and the second timer means. In the arc failure detection device according to any one of claims 1 to 6.
Further provided with a disconnector for the main system connected between the power conditioner and the DC bus, and a disconnector for the branch system connected to the branch system.
The failure determining means is an arc failure detecting device having a function of opening the main system disconnecting switch or the branch system disconnecting switch at the time of arc failure determination.

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